Ok, I have a simple question...
I have an audio interface with a 3 prong plug and a speaker/amp with a 3 prong plug. Both have balanced connections. When I put a one-wire cable between them, only connecting the "hot" leads, everything, to my surprise, worked flawlessly. No noise, no mains hum, no nothing. Connecting the sleeve with a second cable made no difference. I was testing this because I wanted to demonstrate to my students that "current always has to return, so that's why cables have 2 leads: hot and return". Turns out I don't need the return... Luckily I tried it at home first
My guess is that because it's balanced equipment with 3-prong plugs, the audio finds it return-path through the chassis/ground and since my whole studio is grounded from the same place, there can't be too much potential difference between two grounds (none as it seems), so the current return path here is actually earth ground, correct?
When I did the same test with a synth that only has a 2 prong power plug (so no connection to mains ground) and plugged the one-wire cable into the speaker, all I got was mains hum. So I thought: aha, mains hum interference got picked up by the synth (= one large copper plate), couldn't escape to ground (no connection to mains ground on the 2 prong power) and found its way out of the synth towards the ground connection of the speaker, correct?
But why am I, aside from the mains hum, not ALSO hearing the audio? I mean, the current/voltage that sits on my audio output hot lead could also flow towards the speaker and find its way to ground there, no? If mains hum (Europe, 50 Hz) can do it, why can't my audio signal (low note of 100 Hz) do the same thing? This is important for me to thoroughly understand, as I can demonstrate here why you DO need a current return path (cause without current return/second wire all you get is hum...). I'm guessing because ground/reference in my synth is different from ground/reference in the speaker and signal current has no intention to flow between them, does that seem likely?
Thanks.
I have an audio interface with a 3 prong plug and a speaker/amp with a 3 prong plug. Both have balanced connections. When I put a one-wire cable between them, only connecting the "hot" leads, everything, to my surprise, worked flawlessly. No noise, no mains hum, no nothing. Connecting the sleeve with a second cable made no difference. I was testing this because I wanted to demonstrate to my students that "current always has to return, so that's why cables have 2 leads: hot and return". Turns out I don't need the return... Luckily I tried it at home first
My guess is that because it's balanced equipment with 3-prong plugs, the audio finds it return-path through the chassis/ground and since my whole studio is grounded from the same place, there can't be too much potential difference between two grounds (none as it seems), so the current return path here is actually earth ground, correct?
When I did the same test with a synth that only has a 2 prong power plug (so no connection to mains ground) and plugged the one-wire cable into the speaker, all I got was mains hum. So I thought: aha, mains hum interference got picked up by the synth (= one large copper plate), couldn't escape to ground (no connection to mains ground on the 2 prong power) and found its way out of the synth towards the ground connection of the speaker, correct?
But why am I, aside from the mains hum, not ALSO hearing the audio? I mean, the current/voltage that sits on my audio output hot lead could also flow towards the speaker and find its way to ground there, no? If mains hum (Europe, 50 Hz) can do it, why can't my audio signal (low note of 100 Hz) do the same thing? This is important for me to thoroughly understand, as I can demonstrate here why you DO need a current return path (cause without current return/second wire all you get is hum...). I'm guessing because ground/reference in my synth is different from ground/reference in the speaker and signal current has no intention to flow between them, does that seem likely?
Thanks.